1. Field of the Invention
The present invention pertains to cross-linking hardenable resin compositions, metal laminates with cross-linking hardenable resin compositions, and methods for processing metal surfaces with such compounds.
2. Background Art
In recent years, so-called dry film resist has come into widespread use as photo-resist employed in the manufacture of printed circuit boards, where dry film resist generally consists of a photopolymerizable resin composition layer sandwiched between a supporting film layer and a protective film layer. Examples of photopolymerizable resin compositions which have been applied to this type of dry film resist include solvent developing resin compositions and alkali developing resin compositions, the former characterized in that portions thereof that have not been exposed to light can be selectively removed by treatment with a suitable chloro-organic solvent, and the latter characterized in that unexposed portions thereof can be selectively removed using an alkaline aqueous solution. Due to environmental considerations as well as increased costs associated with solvent developing dry film resists, alkali developing dry film resists have come to be the most widely employed.
To use alkali developing dry film resist having a supporting film layer and a protective film layer, first of all, while peeling away the protective film layer from the dry film resist, the surface of the photopolymerizable resin composition layer is heat laminated with a copper clad board, after which a photo-mask is placed on a surface of the protective film layer. The above mentioned photo-mask has a cut-out pattern such that portions of the underlying protective film surface which correspond to areas of the photopolymerizable resin composition layer to be removed are covered by the mask, and portions of the protective film surface corresponding to areas of the photopolymerizable resin composition layer not to be removed are left exposed.
The board is then exposed to ultraviolet light or some other form of radiant energy applicable to the type of photopolymerizable resin composition in use, whereupon photopolymerization and therefore hardening occurs at the portions not covered by the photo-mask. The protective layer is then peeled away after which the board is treated with an aqueous solution of sodium carbonate or some other weakly alkaline aqueous solution thereby effecting development, in other words, removal of the photopolymerizable resin composition at portions which were previously covered by the mask and hence not exposed to ultraviolet light. Thus, by the above described process, a resist pattern is selectively formed on the copper clad board.
For circuit boards with copper through-holes, after etching, the hardened resist pattern is stripped away by treatment with a strong alkaline aqueous solution such as aqueous sodium hydroxide solution, whereby the printed circuit board is obtained. For circuit boards with tin-lead plated through-holes, after tin-lead plating, the hardened resist pattern is stripped away by treatment with strong aqueous base, after which the copper is etched with the tin-lead plating acting as resist, whereby the printed circuit board is obtained.
In the above described processing, it is of course necessary that the dry film resist be able to withstand subsequent etching, plating, and other processes during the manufacture of the printed circuit board. Various studied have been carried out concerning ways to improve the ability of dry film resist to withstand such processing.
In the case of photopolymerizable resin compositions employed in alkali developing dry film resist, many of the resist resin components used in these are hard to the point that when heat laminated to the surface of the copper baseplate of the copper clad board, irregularities in the surface of the copper baseplate are not adequately filled in with the resist resin, thus resulting in the formation of crevices between the resist resin and copper baseplate. In such a case, even though the resist resin components themselves have excellent ability to resist the action of various chemicals, during plating, etching, or other chemical processes, the etching or plating solutions, cleaning or degreasing solvents, etc. can enter into these crevices, progressively penetrating along the interface between the resist resin and copper baseplate, following along continuities between crevices formed therebetween, in this way, finally resulting in short circuits or open circuits in the finished circuit board.
For the above reason, attempts have been made to produce more flexible photopolymerizable resin compositions, so that when lamination is carried out, the resist resin adequately conforms to the surface of the copper baseplate, thereby eliminating the formation of crevices and pockets between the resist resin and copper baseplate, as well as the attendant problems. As a result, adequately flexible photopolymerizable resin compositions have been produced, but with these, the problem referred to as cold flow phenomena occurs, that is, the resist resin components end up being too soft, for which reason there is a tendency for the resin to ooze from the ends of rolls of dry film resist formed therefrom.
For reasons described in the preceding paragraphs, with the various types of conventional dry film resist which have been available up to the present time, none of these conventional dry film resists have been able to simultaneously provide optimal laminating properties as well as improved storage properties with absence of cold flow.